In prior art fluid entangling processes, webs of non-woven fibers are treated with high pressure fluids while supported on apertured patterning screens. Typically, the patterning screen is provided on a drum or continuous conveyor which traverses pressurized fluid jets. Entanglement is effected by employing columnar jet streams which entangle fibers in the web into ordered groups and configurations corresponding to the aperture array in the patterning screen. Non-woven fabrics having MD and CD tensile strengths and randomized structures are produced by action of the jet streams which cause fibers in the web to migrate to apertured or void areas in the screen, entangle and intertwine.
Commercial apparatus which practice this technology generally employ pumping and filtration systems which recirculate fluid from jet streams for reuse. Particular difficulty in high pressure hydroentangling processes is presented by the use of columnar jet streams which are provided by small diameter orifice nozzels. Complex filtration systems are required to remove fiber debris which is dislodged from the web by the high pressure jet streams to prevent clogging of the debris in jet nozzles.
To achieve effective hydroentangling of fibers known processes also employ a variety of carding operations and fiber randomization processes. For example, carded web may be randomized by scrambling and air lay systems prior to entangling.
In conventional entangling processes, air is entrained by high pressure columnar jets which lift the web from the patterning screens resulting in irregularities in the structure of the formed fabric. To counteract this effect, prior art processes employ vacuum systems including, arrangements of slots which are positioned beneath the patterning screen in alignment with the jets to hold the web to the screen. For this same purpose, the art also employs top screens which are placed over the web to restrain its movement.
Vacuum and screen baffling systems of the prior art introduce machine complexity and associated tooling costs. Top screens lower energy efficiency of the entangling process by reducing the energy flux of fluids which impinge upon the web, restricting movement of the fibers. See U.S. Pat. No. 2,862,251 to F. Kalwaites.
Prior art hydroentangling processes for producing patterned non-woven fabrics which employ high pressure columnar jet streams are represented by U.S. Pat. Nos. 3,485,706 and 3,498,874, respectively, to Evans and Evans et al, and U.S. Pat. No. 4,379,799 to Holmes et al.
The present invention is directed to a fluid entangling process and related apparatus for producing novel non-woven fabrics without requirement of the complex machinery of the prior art. Departing from conventional processes, the present invention employs pressurized fan jets with wide diameter outlet orifices to direct divergent fluid sprays to non-randomized fibrous webs. The divergent jets coact with specially configured forming members which support the web. Wide diameter divergent jet nozzles employed in the invention facilitate recirculation of jet streams without requirement of complex filtration systems.
It will be recognized that a process which employs divergent jet streams yields advantages in machinery design and energy efficiencies. The invention departs from the prior art practices which found divergent jets unacceptable for use in entangling processes. The art teaches that divergent sprays entrain excessive air volumes, generating turbulence at web surfaces, yielding non-woven fabrics having non-uniform fiber characteristics. See U.S. Pat. No. 3,498,874 to Evans et al., col. 6, lines 49-75.
Accordingly, it is a broad object of the invention to provide an improved fluid entangling apparatus and related method for production of a variety of novel non-woven fabrics having tensile strength and structural characteristics which advance the art.
A more specific object of the invention is to provide hydroentangling apparatus which is mechanically less complex than employed in prior art processes.
A further object of the invention is to provide a hydroentangling apparatus and process which produce non-woven fabrics having symmetrical structures and MD/CD randomization ratios in the range of 1:1-4:1.
A still further object of the invention is to produce non-wovens having improved tensile strength characteristics employing apparatus and processes which are less complex as compared to the prior art.